1. Field of the Invention
The present invention relates to the field of manufacturing solar cells, and particularly to an apparatus allowing for manufacturing thin film solar cells as well as a method for such manufacturing.
2. Description of the Related Art
Thin film solar cells are usually manufactured by vacuum evaporation of material onto a glass substrate. The Photovoltaic (PV) materials used could be Cu, In, Ga and Se. (Usually called CIGS, CIGSe or CIGS2). Another type is Cu, In and S. (Usually referred to as CIS). A Third type is using Cu, In, Ga, Se and S. (Usually referred to as CIGSS or CIGSS2). Other type of thin film cells using Si or Cd and Te is also possible. Methods of manufacturing vary, but usually include vacuum co-evaporation and sometimes combined with Selenization at high temperature. Other methods used are Close Space Sublimation (CSS) and sputtering.
To improve the efficiency of the cell the substrate is usually heated during the evaporation process. This enables the evaporated atoms and molecules to easier find their place in the crystal structure that is formed on the substrate. To achieve maximum efficiency of a cell the substrates should be heated to 500-600° C. or above. Soda-lime glass cannot be heated to higher than 600° C. and of course not plastic materials either. One can use other glass types, but the Na-content of the soda-lime glass has a positive effect on the structure formation on the glass. So the problem is that the substrate has to be heated during the deposition and if one uses Soda-lime glass with a high Na content it cannot be heated to the optimal temperature. If other materials are used a Na layer first usually is deposited onto the substrate for best result. The temperatures also exclude the use of plastic materials.
The above mentioned method is e.g. disclosed in “Band Gap Profiling and High Speed Deposition of Cu(InGa)Se2 for Thin Film Solar Cells”, Olle Lundberg, Uppsala University, Department of Engineering Sciences, 2003.
U.S. Pat. No. 6,258,620 also describes the above mentioned method, but instead of co-evaporation the CInGa materials are deposited in turn and selenized in a Se flux.